Many polarizers and polarizing beam-splitters are known to the art, each having disadvantages.
The Glan-Thompson polarizer, which is a block of birefringent material cut into prisms and then cemented together acts by reflecting one polarization component at the cement interface and by transmitting the other. The device requires a considerable amount of birefringent material, generally calcite, which is scarce and expensive, and is unable to work with high powered lasers and ultraviolet light, since the light destroys or clouds cement. Furthermore, this beam-splitter, which makes use of the reflected polarization component, suffers from the added disadvantage that polarized beams exit the device at inconvenient angles, for example 45 degrees, when it is often useful that beams are parallel, orthogonal or otherwise oriented.
The Glan-Taylor polarizer which is similar to the Glan-Thompson polarizer but uses an air space instead of cement to separate polarization components can work with many light sources but suffers from reflection loss and ghosting caused by the air gap.
The Wollaston, Rochon and Senarmont beam-splitters, which separates polarization components by transmitting the components through an interface, permit optical contacting for use with most light sources, but produce beams which also exit at inconvenient angles, with one or both polarization components suffering from chromatism and distortion.
The double refracting element (beam displacer), which produces parallel polarized beams of light, achieves small beam separation and limited field. Also, since the beams may pass through a considerable amount of material before achieving useful separation, wavefront distortion can occur in the extraordinary beam due to imperfections in the crystal's structure. (See for example, "Birefringence of Quartz and Calcite," Journal of the Optical Society of America, volume 49, No. 7, July 1959, pages 710-712.) Beam separation can be further limited by the small size and high cost of suitable crystals. Notwithstanding, it is an object of the invention to overcome some of these limitations while using a beam displacing crystal.
Polarizing prisms and their various defects are described in detail by Bennett and Bennett, "Polarization," Handbook of Optics, Driscoll and Vaughan, eds., McGraw-Hill, 1978.
It is an object of this invention, to provide a polarization beam splitter that obviates most of the above mentioned disadvantages of prior art devices; it is yet a further object to provide a device having as its core element a birefringent crystal that is considerably less costly to manufacture than commercially available birefringent crystal based devices. It is yet a further object of the invention to provide a polarization beam splitter that requires a much smaller crystal than conventional commercially available devices that utilized a same type of beam shifting crystal.